Secondhand smoke exposure and associated factors among city residents living in multiunit housing in Bangladesh

Background Secondhand smoke (SHS) poses a high health risk to those living in multiunit housing (MUH) since it can easily spread from unit to unit and throughout the building’s communal areas. MUH residents in Bangladesh are particularly vulnerable to SHS due to the absence of smoking restrictions within a housing complex. Therefore, this study aimed to assess the prevalence of SHS exposure and its associated factors among MUH residents living in seven divisional cities of Bangladesh- Dhaka, Chattogram, Rajshahi, Khulna, Sylhet, Barishal, and Rangpur. Methods From April 2019 to November 2019, a cross-sectional survey was conducted with 616 MUH residents aged 18 or older who had been residing in MUH for at least two years in the seven divisional cities of Bangladesh. A multivariable logistic regression model was performed to determine the associated factors of SHS exposure. Results In MUH complexes, more than half (54.9%) of the 616 respondents were exposed to SHS. The key factors positively associated with SHS exposure were females (aOR: 1.8, 95% CI:1.236–2.681), residents with a low monthly family income (aOR: 1.9, 95% CI: 1.162–3.220), those whose family members smoked (aOR: 2.4, 95% CI: 1.537–3.746), and Dhaka city residents (aOR: 1.9, 95% CI: 1.013–3.440). Conclusions This study revealed a high prevalence of SHS exposure among Bangladeshi MUH residents. Therefore, a smoking ban is needed in and around MUH complexes to protect non-smoking residents from SHS exposure.


Introduction
It is widely recognized that exposure to secondhand smoke (SHS) poses serious health risks for individuals around the world.Both the mainstream smoke breathed by smokers and the sidestream smoke emitted into the environment by burning cigarettes and other tobacco products combine to create SHS [1].Tobacco smoke contains more than 7,000 chemical components, of which at least 250 are known to be harmful to human health [2].There is no safe level of SHS exposure, and even brief exposure can affect human health seriously [3].A large body of epidemiological research has established a link between SHS exposure and increased morbidity and mortality.SHS exposure is a major risk factor for heart disease, stroke, and lung cancer in adults [3][4][5].SHS exposure results in adverse health outcomes in women of reproductive age [6].Children exposed to SHS are at higher risk of bronchitis, pneumonia, asthma, ear infections, and sudden infant death syndrome (SIDS) than those not exposed to SHS [7,8].There are an estimated 1.3 billion tobacco users worldwide, and over 80% of them live in lowand middle-income countries (LMCs) [9].Bangladesh, a lower middle-income country, is one of the world's largest tobacco consumption countries with a smoking prevalence of 18.0% among the adult population [10].Globally, tobacco use causes more than 8 million premature deaths every year, of which around 1.2 million are attributable to SHS exposure [9].A recent study found that in Bangladesh, about 25,000 people die annually due to SHS exposure, and the cost of productivity losses from these premature deaths is estimated at BDT 39.27 billion [11].
Bangladesh is one of the most densely populated countries in the world with a 38.9% urban population [12].To meet the housing needs of an increasing urban population, multiunit housing (MUH) has become the country's largest housing option.MUH is a residential building consisting of at least two separate units with shared areas, including common building entrance, elevators, stairs, basements, lobbies, parking areas, waiting spaces, and roofs.MUH residents in the country are particularly vulnerable to SHS exposure because there is no provision to restrict smoking at home and inside residential buildings.However, in recent years, some developed nations, such as the United States of America, Canada, and Australia have adopted smoke-free housing policies to protect their MUH residents from involuntary exposure to SHS [13][14][15].Existing evidence indicates that the implementation of smoke-free housing policies not only reduces SHS exposure but also increases smoking cessation among MUH residents [16].
Bangladesh is the signatory of the WHO Framework Convention on Tobacco Control (FCTC) and enacted the 'Smoking and Tobacco Products Usage (Control) Act 2005' in line with the FCTC [17].The definition of public place and public transport was widened through an amendment of the Act in 2013, but there was no provision in the amendment to restrict smoking in the common spaces of a multiunit housing complex.Furthermore, there is a national housing policy that has not restricted tobacco smoking at home and inside housing complexes [18].Consequently, housing residents can smoke anywhere in MUH complexes.
In Bangladesh, 39.0% of adults (equivalent to 40.8 million) are exposed to SHS at home due to smoking by family members and visitors [10].This prevalence does not represent the overall prevalence of SHS exposure in a residential setting because this refers to only smoking at home.Available literature shows that housing residents are also exposed to SHS from other sources like neighbouring units, common areas, and adjacent buildings [19,20].Therefore, this study aimed to assess the prevalence of SHS exposure among city residents at home and from neighbouring units, common areas, and next buildings in the seven divisional cities of Bangladesh-Dhaka, Chattogram, Rajshahi, Khulna, Sylhet, Barishal, and Rangpur as well as identify its associated factors.

Study design and participants
During the months of April and November of 2019, MUH residents from the seven divisional cities participated in a cross-sectional study.Adults (18+) with a minimum 2-year residency in multiunit housing were eligible to participate.Pregnant women and people with speech and/ or hearing difficulties were not included in this study.

Measures
Basic information.Self-reported basic variables included sex (male or female), age (18-39, 40-59, or �60 years), marital status (single or ever married), education level (primary, secondary, higher secondary, or tertiary), occupation (job holder, business, student, retired, or housewife), religion (Muslim, Hindu, or Buddhist), monthly family income (<50,000 BDT, 50,000-99,000 BDT, or �100,000 BDT), smoking status (smoker or non-smoker), smoking by family members (yes or no), length of stay at home (�12 hours or >12 hours), type of housing complex (private or government), place of residence (Dhaka city, Chattogram city, Rajshahi city, Khulna city, Sylhet city, Barishal city, or Rangpur city).The smoking status of the respondents was determined by asking, "On how many days during the past 30 days, did you smoke cigarettes/bidis?"Those who smoked cigarettes/bidis on at least one day during the past 30 days were categorized as 'smokers', and on the other hand, those who did not smoke cigarettes/bidis during the past 30 days were categorized as 'non-smokers' [21].
SHS exposure.Self-reported SHS exposure was assessed using the question, "On how many days during the past 30 days, did you get the smell of cigarettes/bidis from the following places: (a) your own flats, (b) next flats, (c) common spaces and (d) next buildings?"Those who reported any number between 1 and 30 days were considered exposed to SHS from the particular place [22].In this study, overall SHS exposure within MUH complexes was the outcome variable and was defined as exposure from at least one of these places-own flats, next flats, common spaces and next buildings during the past 30 days.
Sample size calculation and distribution.The minimum required sample size for this study was calculated using a single population proportion formula, n = ðz a=2 Þ2pð1À pÞ e 2 [23], where n = desired sample size, z = standard normal deviate = 1.96 at 95% confidence interval, p = prevalence of SHS exposure (unknown) among city residents living in MUH in the divisional cities of Bangladesh = 50%, and e = margin of error = 4%.This yielded a sample size of 600.
The number of MUH complexes in Dhaka city is much higher than that in any other city in the country.Therefore, we allocated about one-third of the sample to Dhaka city and distribute the remaining two-thirds among the six cities equally.There was no published list of MUH complexes in Bangladesh.Taking budget constraints into account, we randomly selected ten wards from each of the seven cities and prepared a city-wise list of all MUH complexes in the selected wards.We did not include solely-owned MUH complexes in the list because those did not have a housing management committee.The list included 1,067 MUH complexes from Dhaka city, 210 from Chattogram city, 120 from Rajshahi city, 95 from Khulna city, 90 from Sylhet city, 80 from Barishal city, and 105 from Rangpur city.With a plan to enroll three to five respondents from each MUH complex, we randomly selected 60 complexes from Dhaka city and 20 complexes from each of the six cities.Finally, we interviewed a total of 616 respondents, including 214 from Dhaka city and 67 from each of the six cities.
Training and pretesting.For data collection for this study, we recruited six teams of experienced field staff with a social science background.Each team consisted of three members-one male data collector, one female data collector, and one male field supervisor.Before data collection, they were given two-day training so that they could thoroughly understand the objectives and methodology of the study and the survey questionnaire.They were also taught the techniques of rapport building, environment control, maintaining neutrality, and obtaining informed consent from the respondents.However, a semi-structured questionnaire was first developed in English, and it was forward-translated into the local language Bengali and back-translated into English by two bilingual translators to ensure the accuracy of the contents [24].Following the training, the Bengali version questionnaire was pretested among 25 respondents in similar study settings to determine its clarity, practicality, and relevance to the study participants.The questionnaire was finalized after necessary modifications based on the findings of the pretest.
Fieldwork.First of all, the field supervisors approached the housing management committees of the selected complexes with an official letter seeking permission for data collection.After obtaining permission, the data collectors accompanied by the field supervisors visited the housing complexes and informed the guards on duty about the purpose of their visit.The guards introduced the data collectors with the residents available in their units via intercom, and subsequently the data collectors explained the objectives of the study to them.Those who consented to participate in the study were met by the data collectors and interviewed using a semi-structured survey questionnaire.A total of three to five residents from each MUH complex, including one resident from each unit were purposively selected for the face-to-face interviews.In case of two-unit MUH complexes, we recruited a maximum of two residents from each unit.These face-to-face interviews were held either in the respondents' houses or in the waiting areas of the complexes during the daytime on both weekdays and weekends.An interview lasted for approximately 20 minutes.Each completed questionnaire was spot-checked by the field supervisors to assess the accuracy, completeness, and consistency of the data collected.Furthermore, the principal investigator and the co-investigator visited the study sites during data collection to ensure the data were collected properly.The respondents were not given any financial benefits for participating in the study.
Statistical analysis.Data analysis was performed using SPSS statistical software version 25.0.For descriptive statistics, frequencies and percentages were used to describe the basic characteristics of the respondents.Bivariate analyses were done using the chi-square test of independence for categorical variables.All independent variables were included in the binary logistic regression model, and the backward stepwise selection method was used to identify the factors associated with SHS exposure within MUH complexes.Associations between the outcome variable and the factors were presented as adjusted odds ratios (aOR) at 95% confidence intervals (CIs).Model fitness was assessed by using the Hosmer-Lemeshow test with a p-value of 0.509.Multicollinearity was checked by examining the standard errors (SEs) of regression coefficients in the logistic regression analyses.An SE with a range of 0.001 to 5.0 suggests that there is no multicollinearity among independent variables [25].The SEs for the independent variables in our adjusted model were between 0.198 and 0.372, indicating the absence of multicollinearity.All statistics were tested using a two-sided test, and a p value of <0.05 was considered statistically significant.
Ethical considerations.Ethical clearance was obtained from the National Research Ethics Committee following the ethical guidelines of the Bangladesh Medical Research Council (BMRC) (Reference number: 25003092019).Written informed consent was taken from the respondents.The informed consent form clearly explained the aims and procedures of the study, the risks and benefits associated with participation, their right to voluntary participation and their right to withdraw from the study, and the anonymity and confidentiality of their data.

Characteristics of the respondents
Table 1 displays the demographic breakdown of the 616 respondents.Males made up the majority (66.7%) of the respondents, and those between the ages of 40 and 59 made up the largest age group, followed by those between the ages of 18 and 39 (43.7%).By marital status, 85.4% were ever married, and 14.6% were single.About two-thirds of the respondents completed Bachelor's degree or higher education, while about a third had secondary education.Most of the respondents (44.6%) were job holders, while 20.3% were housewives.In terms of

Frequency of daily SHS exposure
Fig 2 shows the frequency of daily SHS exposure from different places among MUH residents during the last 30 days.Among the respondents who reported daily SHS exposure in MUH complexes, most were exposed to SHS 1 to 3 times a day from next flats (75.0%), followed by common spaces (62.9%), and next buildings (55.0%).On the other hand, about three-fifths (58.6%) of the respondents who experienced daily SHS exposure in their own flats were exposed to SHS 4 to 7 times a day.

Associations between SHS exposure and characteristics
According to the results of bivariate analysis shown in Table 2, sex, occupation, length of stay at home, smoking status, smoking by family members, and place of residence were found to be associated with SHS exposure in MUH complexes.SHS exposure was higher among the respondents who were female, housewives, stayed at home for more than 12 hours per day, were smokers, had smoking family members, and resided in Dhaka city.

Predictors of SHS exposure within MUH complexes
The results of multivariable logistic regression analysis are provided in Table 3.By the sex category, females were 1.8 times more likely to be exposed to SHS within MUH complexes than their male counterparts (95% CI = 1.236-2.681).The respondents with a monthly family income of below 50,000 BDT had a 1.9 times higher chance of being exposed to SHS within MUH complexes than those having a monthly family income of 100,000 BDT or more (95% CI = 1.162-3.220).Smokers were 2.6 times more likely to be exposed to SHS within MUH complexes than their non-smoking counterparts (95% CI = 1.643-4.252).The respondents whose family members were smokers had a 2.4 times higher chance of being exposed to SHS within MUH complexes compared to those whose family members were not smokers (95% CI = 1.537-3.746).Furthermore, the residents of Dhaka city were at 1.9 times higher risk of experiencing SHS exposure within MUH complexes than those from Rangpur city (95% CI = 1.013-3.440).

Discussion
We carried out this study to investigate the prevalence of SHS exposure and its associated factors among MUH residents in the seven Bangladeshi divisional cities.Over half (54.9%) of the respondents living in MUH where there was no smoke-free policy were exposed to SHS within MUH complexes during the last month.This prevalence of SHS exposure is higher than that reported in other studies.A study conducted in New York State showed that 46.2% of residents living in MUH with a smoke-free home policy experienced SHS incursions in their units from somewhere else in or around their buildings during the last 12 months [26].Another US study found that 49.9% of MUH residents who followed smoke-free home rules reported SHS incursions into their units, which originated in neighbouring units, common areas, or adjacent buildings during the last 12 months [27].The higher prevalence of SHS exposure in Bangladesh could be mainly due to the absence of smoke-free home policies in MUH complexes.However, the findings suggest the need to implement a comprehensive smoke-free policy in MUH complexes to fully protect residents from exposure to SHS.In adherence to the tobacco control legislation, Bangladesh has implemented prohibitions on smoking in numerous public venues and on public transportation.Given the significant extent of SHS exposure, it is within the purview of the government to potentially enact legal measures to prohibit tobacco smoking within MUH complexes.Moreover, the government's dedication to establishing a tobacco-free Bangladesh by the year 2040 possesses the capacity to guarantee the existence of smoke-free surroundings within residential areas, which serves as a significant contributor to SHS exposure among individuals who do not engage in smoking activities.
In the present study, females were more likely to be exposed to SHS within housing complexes than males.This finding is supported by prior research conducted in Bangladesh and other Asian countries [28][29][30].The majority of Bangladeshi females are housewives who spend most of their time inside housing complexes, particularly at home.Due to their prolonged stay inside complexes, they may have been at increased risk of SHS exposure at home and from neighbouring units, common areas, and adjacent buildings.
The present study revealed that the respondents from a low-income group had a higher risk of experiencing SHS exposure within MUH complexes compared to those from a high-income group.Similar findings have been observed in previous studies conducted in China, Kuwait, and the United States of America [31][32][33].One possible explanation for this higher prevalence of SHS exposure is that households with a low income live in small flats where one room is attached to another so closely that non-smoking family members are easily exposed to tobacco smoke when other members smoke inside flats [34,35].
The present study showed that smoking residents had higher odds of being exposed to SHS within MUH complexes than their non-smoking counterparts.This finding is congruent with previous studies conducted in Malaysia and Portugal [36,37].The higher prevalence of SHS exposure can be explained by the fact that residents who smoke are more likely to have friendships with smoking residents compared to non-smoking residents, and therefore have a higher risk of being exposed to SHS [38].Furthermore, smokers are less likely to perceive SHS as harmful than non-smokers, and this may have discouraged them to avoid SHS exposure [39].
According to the results of the present study, MUH residents whose family members smoked were more likely to be exposed to SHS within housing complexes than those whose family members did not smoke.This finding is consistent with several earlier investigations done in Bangladesh and other countries [28,40,41].Due to lack of smoking restrictions, many people smoke in their homes, which leads to increased exposure to SHS among non-smoking family members [42].
Among the respondents, those living in Dhaka city had the highest exposure to SHS within housing complexes.Evidence shows that a large portion of land owners in Dhaka city do not maintain an adequate distance from one building to another [43,44].Because of the shorter inter-building distance, MUH residents in Dhaka city may have experienced more SHS incursions from adjacent buildings than those in other cities in Bangladesh.

Limitations
This research has a number of drawbacks.First, due to the cross-sectional design, causal relationships between the outcome variable and the independent variables could not be established in this study.Second, all data were self-reported by the participants, which could have led to recollection and social desirability bias.Third, SHS exposure was evaluated based on the ability to smell SHS.This evaluation may have led to disparities between perceived and true SHS exposure levels.Fourth, this study recruited more male respondents than female ones, which may have biased the results.In the cultural context of Bangladesh, it is commonly observed that women often experience a sense of embarrassment when engaging in conversation with unknown individuals, particularly those of the male gender.Another concern, namely that of security, might have deterred women from independently opening doors when their male or elderly family members were not present at home.Hence, more male residents agreed to participate in the interviews than their female counterparts.Finally, we did not collect data regarding the number of units within sampled MUH complexes.The quantity of SHS exposure frequently varies depending on the number of units in a complex; thus, we recognize that it could be crucial to determine the number of units inside sampled complexes.In a complex with more units, there are more residents.Similar to this, a complex with more occupants will likely have more smokers.The likelihood that smokers will smoke in communal spaces increases with the number of smokers in the complex, putting non-smokers at increased risk of SHS exposure.We were unable to demonstrate how the number of units in a MUH complex affected the level of SHS exposure among non-smoking inhabitants due to lack of information on the number of units.

Conclusions
The present study revealed a high prevalence of SHS exposure among MUH residents living in the divisional cities of Bangladesh.SHS exposure was significantly related with females, low income groups, smokers, those with smoking family members, and Dhaka city residents.The findings indicate an urgent need to minimize SHS exposure among MUH residents across the country.To protect non-smoking residents from SHS exposure, the Government of Bangladesh should adopt a smoking ban in and around housing complexes through revisions in the current tobacco control law and the national housing policy.Furthermore, cessation services, such as behavioural counselling and pharmacotherapy can be introduced in MUH complexes so that smokers are able to quit smoking quickly.residents.Finally, the authors highly appreciate the hard work and dedication of the field supervisors and data collectors.

Table 1 . Distribution of the respondents by characteristics (n = 616).
0% of the respondents said their family made between 50,000 and 99,000 BDT per month, while 35.1% said they made less than 50,000 BDT per month.The majority (53.2%) of the respondents spent 12 hours or less a day at home during the past 30 days, 46.8% spent more than 12 hours a day at home during the past 30 days.By type of housing complex, more than three-fourths of the respondents resided in private MUH complexes.Over a third of the respondents (34.7%) were from Dhaka city, while 10.9% were from each of the other six divisional cities-Chattogram, Rajshahi, Khulna, Sylhet, Barishal, and Rangpur.